Power transmission system

ABSTRACT

A power transmission system includes a control device that controls a motor generator, a synchronizing mechanism, and a clutch mechanism such that at least one of the synchronizing mechanism and the clutch mechanism constantly transmits power between a first shaft and a second shaft during a gear switch from a first-speed gear to a second-speed gear and the motor generator constantly generates torque for a period from operation start of each of the synchronizing mechanism and the clutch mechanism to a power transmission state of the synchronizing mechanism.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2018-059035, filed Mar. 26, 2018, theentire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a power transmissionsystem.

BACKGROUND

Conventionally, transmissions include an input shaft, an output shaft,multiple gears including a drive gear rotatably attached to the inputshaft and a driven gear fixed to the output shaft, and a clutchmechanism for selecting a gear to which power is transmitted (disclosedin Japanese Laid-open Patent Application Publication No. 2013-24391 andGerman Patent Application Publication No. DE 102013108300 A1, forexample).

Such a transmission is placed in neutral state to transmit no power, atthe time of a gear switch for the acceleration of a vehicle, forexample. This may drastically change the acceleration of the vehicle,exerting impact on the vehicle.

An object of the present invention is to provide a power transmissionsystem that can prevent a vehicle from being affected by impact due to agear switch, for example.

SUMMARY

In general, according to one embodiment, a power transmission systemincludes a transmission that is located between a motor generator and awheel both of which are mounted on a vehicle, and a control device. Thetransmission includes a first shaft that is rotatable; a second shaftthat is rotatable and parallel to the first shaft; a first-speed gearhaving a first gear and a second gear, the first gear rotatably attachedto the first shaft, the second gear attached to the second shaft to meshwith the first gear and integrally rotate with the second shaft; asecond-speed gear being smaller in gear ratio than the first-speed gearand having a third gear and a fourth gear, the third gear rotatablyattached to the first shaft, the fourth gear attached to the secondshaft to mesh with the third gear and integrally rotate with the secondshaft; a synchronizing mechanism that is interposed between the firstshaft and the third gear and to be switched between a power transmissionstate and a power shut-off state, the power transmission state being astate in which the synchronizing mechanism generates friction force thatcauses a rotation speed of the first shaft and a rotation speed of thethird gear to approach each other, the power shut-off state being astate in which the synchronizing mechanism generates no friction force;and a clutch mechanism that switches transmission and non-transmissionof rotation between the first shaft and the first gear and between thefirst shaft and the third gear. One of the first shaft and the secondshaft is connected to the motor generator and the other is connected tothe wheel. The control device controls the motor generator, thesynchronizing mechanism, and the clutch mechanism such that at least oneof the synchronizing mechanism and the clutch mechanism constantlytransmits power between the first shaft and the second shaft during agear switch from the first-speed gear to the second-speed gear, and thatthe motor generator constantly generates torque for a period from wheneach of the synchronizing mechanism and the clutch mechanism startsoperating to when the synchronizing mechanism is placed in the powertransmission state.

With such a configuration, for example, at least one of the clutchmechanism and the synchronizing mechanism constantly transmits the powerof the motor generator between the first shaft and the second shaftduring a gear switch from the first-speed gear to the second-speed gearand the motor generator constantly generates the torque for the periodfrom when each of the synchronizing mechanism and the clutch mechanismstarts operating to when the synchronizing mechanism is placed in thepower transmission state. This can prevent the vehicle from beingaffected by impact due to the gear switch. Also, the acceleration of thevehicle can be prevented from falling to zero at the time of a gearswitch from the first-speed gear to the second-speed gear while thevehicle is accelerating.

According to the power transmission system, for example, thesynchronizing mechanism includes a first cone face of the third gear,that integrally rotates with the third gear; a synchronizer ring havinga second cone face that is pressed against the first cone face togenerate friction force with the first cone face; and a first sleevethat is movable along an axis of the first shaft between a pressposition and a non-press position, and integrally rotates with the firstshaft. The press position is a position in which the second cone face ispressed against the first cone face. The non-press position is aposition in which the second cone face is not pressed against the firstcone face. The first sleeve is movable from the non-press position tothe press position while the clutch mechanism transmits rotation betweenthe first shaft and the first gear and transmits no rotation between thefirst shaft and the third gear. The clutch mechanism is configured totransmit rotation between the first shaft and the first gear while thefirst sleeve moves from the non-press position to the press position.

With such a configuration, for example, the first sleeve is movable tothe press position from the non-press position while the clutchmechanism transmits rotation between the first shaft and the first gearand transmits no rotation between the first shaft and the third gear,and the clutch mechanism can transmit rotation between the first shaftand the first gear while the first sleeve moves from the non-pressposition to the press position. This makes it possible to prevent notransmission of the power between the first shaft and the second shaftat the time of a gear switch from the first-speed gear to thesecond-speed gear for acceleration of the vehicle.

According to the power transmission system, for example, the first shaftand the first gear are rotated in a first direction by power of themotor generator. The clutch mechanism includes a one-way clutch that islocated between the first shaft and the first gear, transmits rotationin the first direction from the one of the first shaft and the secondshaft to the other, and allows the other to rotate in the firstdirection relative to the one of the first shaft and the second shaft.

With such a configuration, the one-way clutch can transmit rotationbetween the first shaft and the first gear while the first sleeve movesfrom the non-press position to the press position.

According to the power transmission system, for example, the first-speedgear and the second-speed gear are spaced apart from each other alongthe axis of the first shaft. The clutch mechanism includes first teeththat integrally rotate with the first gear; second teeth that integrallyrotate with the third gear; a first movable part that includes thirdteeth, is located between the first gear and the third gear, is movablealong the axis of the first shaft between a first mesh position and afirst non-mesh position, and integrally rotates with the first shaft,the first mesh position being a position in which the third teeth andthe first teeth mesh with each other, the first non-mesh position beingcloser to the third gear than the mesh position and being a position inwhich the third teeth and the first teeth do not mesh with each other; asecond movable part that includes fourth teeth, is located between thefirst gear and the third gear, is movable along the axis of the firstshaft between a second mesh position and a second non-mesh position andintegrally rotates with the first shaft, and presses the second coneface against the first cone face while moving from the second non-meshposition to the second mesh position, the second mesh position being aposition in which the fourth teeth and the second teeth mesh with eachother, the second mesh position being closer to the first gear than themesh position, and being a position in which the fourth teeth and thesecond teeth do not mesh with each other; and a driver that connects thefirst movable part and the second movable part, generates force to movethe first movable part to the first non-mesh position when the firstmovable part is located in the first mesh position and the secondmovable part is located in the second non-mesh position, and moves thefirst movable part to the non-mesh position by the force along with themotion of the second movable part to the second mesh position to pressthe second cone face against the first cone face.

With such a configuration, the first movable part can transmit rotationbetween the first shaft and the first gear while the first sleeve movesfrom the non-press position to the press position.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exemplary diagram illustrating the schematic configurationof a vehicle in a first embodiment;

FIG. 2 is an exemplary block diagram illustrating the schematicconfiguration of the vehicle in the first embodiment;

FIG. 3 is an exemplary timing chart illustrating an example of theoperation of the vehicle in the first embodiment;

FIG. 4 is an exemplary diagram illustrating the schematic configurationof a vehicle in a second embodiment; and

FIG. 5 is an exemplary diagram illustrating the schematic configurationof a vehicle in a third embodiment.

DETAILED DESCRIPTION

Hereinafter, exemplary embodiments of the present invention will bedisclosed. In the present specification, ordinal numbers are used fordistinguishing parts, locations, and the like, and not intended toindicate order or priority. The following embodiments include like orsame components. Common reference numerals denote the same or likecomponents and redundant description thereof is omitted.

First Embodiment

FIG. 1 is an exemplary diagram illustrating the schematic configurationof a vehicle 1 in a first embodiment. As illustrated in FIG. 1, thevehicle 1 includes a motor generator 11 as a driving source, atransmission 12, wheels 13L and 13R being driving wheels, and wheels(not illustrated) being driven wheels. The power of the motor generator11 is transmitted to the wheels 13L and 13R through the transmission 12to rotate the wheels 13L and 13R, whereby the vehicle 1 runs.

The motor generator 11 includes a shaft 11 a and a case lib. The shaft11 a is rotatably supported by the case 11 b about a first rotationalcenter Ax1. The case 11 b is supported by a body (not illustrated) ofthe vehicle 1. The case 11 b accommodates a rotor (not illustrated) thatrotates integrally with the shaft 11 a and a stator (not illustrated)surrounding the outer circumference of the rotor. Applied with a voltage(current), the motor generator 11 applies torque (power) to the shaft 11a about the first rotational center Ax1.

The transmission 12 is located between the motor generator 11 being aninput and the wheels 13L and 13R being an output. The transmission 12,while coupled to the motor generator 11, is supported by the vehiclebody.

The transmission 12 includes an input shaft 21, an output shaft 22, aplurality of gears 30, a gear connection mechanism 23, and a case 24.The case 24 accommodates the input shaft 21, the output shaft 22, thegears 30, and the gear connection mechanism 23. The case 24 is supportedby the vehicle body. The input shaft 21 is an example of a first shaftand the output shaft 22 is an example of a second shaft.

The input shaft 21 and the output shaft 22 are spaced apart from eachother in parallel. The input shaft 21 is rotatably supported by the case24 about the first rotational center Ax1 while the output shaft 22 isrotatably supported by the case 24 about a second rotational center Ax2.The first rotational center Ax1 and the second rotational center Ax2 arealso referred to as rotational axes.

The input shaft 21 is connected to the shaft 11 a of the motor generator11 and rotates integrally with, that is, simultaneously with the shaft11 a. Hereinafter, the direction of the rotation of the input shaft 21when the vehicle 1 travels forward is referred to as a normal direction.The shaft 11 a and the input shaft 21 does not need to be directlyconnected to each other and another rotation transmitting member such asa gear, a coupling, and a belt may be interposed therebetween. The shaft11 a and the input shaft 21 may not rotate at the same speed.

The gears 30 are constantly meshing gears and extend across the inputshaft 21 and the output shaft 22. The gears 30 differ in gear ratio(reduction ratio). The gears are also referred to as gear pairs.

The gears 30 include a 1-speed gear 31 and a 2-speed gear 32. The1-speed gear 31 and the 2-speed gear 32 are spaced from each other alongthe first rotational center Ax1 of the input shaft 21. The 2-speed gear32 is lower in gear ratio than the 1-speed gear 31. The 1-speed gear 31is also referred to as a low gear and the 2-speed gear 32 is alsoreferred to as a high gear.

The 1-speed gear 31 includes a drive gear 33 and a driven gear 34 thatmesh with each other, and the 2-speed gear 32 includes a drive gear 35and a driven gear 36 that mesh with each other. The drive gear 33 is anexample of a first gear, the driven gear 34 is an example of a secondgear, the drive gear 35 is an example of a third gear, and the drivengear 36 is an example of a fourth gear.

The drive gears 33 and 35 are supported by the input shaft 21 throughbearings (not illustrated) and rotate about the first rotational centerAx1 relative to the input shaft 21. Movement of the drive gears 33 and35 along the first rotational center Ax1 is limited.

The transmission 12 further includes a one-way clutch 37 between thedrive gear 33 of the 1-speed gear 31 and the input shaft 21. The one-wayclutch 37 prohibits the input shaft 21 from normally rotating relativeto the drive gear 33. The one-way clutch 37 can thus transmit normalrotation from the input shaft 21 to the drive gear 33. The one-wayclutch 37 permits the drive gear 33 to normally rotate relative to theinput shaft 21. The power of the motor generator 11 is transmitted tothe drive gear 33 from the input shaft 21 through the one-way clutch 37to rotate the input shaft 21 and the drive gear 33 in the normaldirection. The normal direction is an example of a first direction.

The driven gears 34 and 36 are fixed to the output shaft 22 and rotateabout the second rotational center Ax2 integrally with the output shaft22.

The output shaft 22 is provided with a final gear 38. The final gear 38is fixed to the output shaft 22 to rotate together about the secondrotational center Ax2. The final gear 38 meshes with a differential ringgear 39 a located in the case of a differential gear 39. Thedifferential gear 39 is connected to the wheels 13L and 13R throughdrive shafts 40L and 40R.

The gear connection mechanism 23 includes a clutch mechanism 41 and asynchronizing mechanism 42. The clutch mechanism 41 and thesynchronizing mechanism 42 are separated from each other. That is, theclutch mechanism 41 and the synchronizing mechanism 42 operateindependently of each other.

The clutch mechanism 41 is located between the drive gear 33 of the1-speed gear 31 and the drive gear 35 of the 2-speed gear 32. Thesynchronizing mechanism 42 is opposite to the drive gear 33 across thedrive gear 35. Thus, the drive gear 35 is placed between the clutchmechanism 41 and the synchronizing mechanism 42.

The clutch mechanism 41 is a dog clutch mechanism that selectivelyswitches connection (coupled) and disconnection (non-coupled) betweenthe input shaft 21, and the drive gear 33 of the 1-speed gear 31 and thedrive gear 35 of the 2-speed gear 32. That is, the clutch mechanism 41switches the transmission and non-transmission of rotation between theinput shaft 21 and the drive gear 33 and between the input shaft 21 andthe drive gear 35.

The clutch mechanism 41 includes a hub 43 and a sleeve 44. The clutchmechanism 41 includes the one-way clutch 37 as well. The hub 43 iscoupled to the input shaft 21 and rotates about the first rotationalcenter Ax1 integrally with the input shaft 21. The sleeve 44 is coupledto the hub 43 by spline coupling, rotates about the first rotationalcenter Ax1 integrally with the hub 43, and is movable along the axis ofthe input shaft 21 relative to the hub 43. Thus, the sleeve 44 rotatesabout the first rotational center Ax1 integrally with the input shaft 21and is movable along the axis of the input shaft 21.

The sleeve 44 is located between the drive gear 33 of the 1-speed gear31 and the drive gear 35 of the 2-speed gear 32. The sleeve 44 is anexample of a second sleeve.

The sleeve 44 includes teeth 44 a and teeth 44 b. The teeth 44 a arelocated on one end (right-side end in FIG. 1) of the sleeve 44 closer tothe drive gear 33 and are aligned about the first rotational center Ax1.The teeth 44 a can mesh with teeth 33 a of the drive gear 33. The teeth33 a are located on part (left-side part in FIG. 1) of the drive gear 33closer to the sleeve 44 to integrally rotate with the drive gear 33. Theteeth 44 b are located on one end (left-side end in FIG. 1) of thesleeve 44 closer to the drive gear 35 and are aligned about the firstrotational center Ax1. The teeth 44 b can mesh with teeth 35 a of thedrive gear 35. The teeth 35 a are located on part (right-side part inFIG. 1) of the drive gear 35 closer to the sleeve 44 to integrallyrotate with the drive gear 35. The teeth 33 a, 35 a, 44 a, and 44 b aredog teeth. The teeth 33 a are an example of first teeth, the teeth 35 aare an example of second teeth, the teeth 44 a are an example of thirdteeth, and the teeth 44 b are an example of fourth teeth.

The sleeve 44 is movable along the axis of the input shaft 21 relativeto the input shaft 21. To be specific, the sleeve 44 is movable to a1-speed mesh position (not illustrated), a non-mesh position (FIG. 1),and a 2-speed mesh position (not illustrated).

In the non-mesh position (FIG. 1) the teeth 44 a of the sleeve 44 andthe teeth 33 a of the drive gear 33 do not mesh with each other, and theteeth 44 b of the sleeve 44 and the teeth 35 a of the drive gear 35 donot mesh with each other. The 1-speed mesh position is closer to thedrive gear 33 (right side in FIG. 1) than the non-mesh position, and inthe 1-speed mesh position the teeth 44 a of the sleeve 44 and the teeth33 a of the drive gear 33 mesh with each other. The 2-speed meshposition is closer to the drive gear 35 (left side in FIG. 1) than thenon-mesh position, and in the 2-speed mesh position the teeth 44 b ofthe sleeve 44 and the teeth 35 a of the drive gear 35 mesh with eachother. That is, the sleeve 44 is not coupled to the drive gear 33 andthe drive gear 35 in the non-mesh position, is coupled to the drive gear33 in the 1-speed mesh position, and is coupled to the drive gear 35 inthe 2-speed mesh position. The non-mesh position is also referred to asa neutral position.

While the sleeve 44 moves from the non-mesh position (FIG. 1) to the2-speed mesh position (left side in FIG. 1), the sleeve 48 presses asynchronizer ring 49 toward the drive gear 35 to press a cone face 49 bof the synchronizer ring 49 against a cone face 35 b of the drive gear35.

A first movement mechanism 45 can selectively move the sleeve 44 to anyof the 1-speed mesh position with the drive gear 33, the 2-speed meshposition with the drive gear 35, and the non-mesh position. The firstmovement mechanism 45 includes an actuator 45 a (FIG. 2) such as a motorand a transmission mechanism (not illustrated) that transmits drivingpower of the actuator 45 a to the sleeve 44.

In the 1-speed mesh position where the sleeve 44 meshes with the drivegear 33, the input shaft 21 and the drive gear 33 are integrallyrotatable. This forms a 1-speed transmission path from the input shaft21 to the drive shafts 40L and 40R through the drive gear 33, the drivengear 34, the output shaft 22, the final gear 38, and the differentialgear 39. In the first embodiment, the one-way clutch 37 also works tointegrally rotate the input shaft 21 and the drive gear 33 in the normaldirection. Thus, both of the one-way clutch 37 and the clutch mechanism41 transmit rotation (power) from the input shaft 21 to the drive gear33 while the vehicle 1 travels forward. A ratio of the power transmittedby the one-way clutch 37 and the power transmitted by the clutchmechanism 41 is set arbitrarily. The clutch mechanism 41 may transmit nopower while the sleeve 44 is located at the 1-speed mesh position duringthe forward travel of the vehicle 1. The one-way clutch 37 transmits nopower and the clutch mechanism 41 transmits power to the drive gear 33from the input shaft 21 while the vehicle 1 travels backward.

In the 2-speed mesh position where the sleeve 44 meshes with the drivegear 35, the input shaft 21 and the drive gear 35 are integrallyrotatable. This forms a 2-speed transmission path from the input shaft21 to the drive shafts 40L, 40R through the drive gear 35, the drivengear 36, the output shaft 22, the final gear 38, and the differentialgear 39.

As described above, the clutch mechanism 41 can be selectively switchedto a 1-speed mesh state, a 2-speed mesh state, and a non-mesh state, Inthe 1-speed mesh state the teeth 44 a of the sleeve 44 mesh with theteeth 33 a of the drive gear 33 of the 1-speed gear 31 to integrallyrotate the input shaft 21 and the drive gear 33. In 2-speed mesh statethe teeth 44 b of the sleeve 44 mesh with the teeth 35 a of the drivegear 35 of the 2-speed gear 32 to integrally rotate the input shaft 21and the drive gear 35. In the non-mesh state the teeth 44 a and theteeth 33 a as well as the teeth 44 b and the teeth 35 a do not mesh witheach other to allow the input shaft 21 and each of the drive gear 33 andthe drive gear 35 to relatively rotate. To be specific, in the non-meshstate the one-way clutch 37 allows the drive gear 33 to normally rotaterelative to the input shaft 21.

The synchronizing mechanism 42 is interposed between the input shaft 21and the drive gear 35. The synchronizing mechanism 42 is switchedbetween a power transmission state (friction generation) and a powershut-off state (non-friction generation). In the power transmissionstate the synchronizing mechanism 42 generates friction force so thatthe rotation speed of the input shaft 21 and the rotation speed of thedrive gear 35 approach each other. In the power shut-off state thesynchronizing mechanism 42 generates no friction force. Thesynchronizing mechanism 42 can synchronize the rotation of the drivegear 35 and the rotation of the input shaft 21 through the frictionforce.

The synchronizing mechanism 42 includes a hub 47, a sleeve 48, and thesynchronizer ring 49. The hub 47, the sleeve 48, and the synchronizerring 49 are opposite to the sleeve 44 and the drive gear 33 across thedrive gear 35. The sleeve 48 is an example of a first sleeve.

The synchronizer ring 49 is interposed between the sleeve 48 and thedrive gear 35 and is rotatable relative to the drive gear 35 and movablealong the axis of the input shaft 21.

The synchronizer ring 49 includes a pressed part 49 a and the cone face49 b. The pressed part 49 a is an annular flat face about the firstrotational center Ax1. The pressed part 49 a can contact with the sleeve48 and is pressed by the sleeve 48. The cone face 49 b cancircumferentially slide with the cone face 35 b of the drive gear 35,which rotate together, about the first rotational center Ax1. The sleeve48 presses the cone face 49 b against the cone face 35 b to generatefriction force therebetween. The cone face 35 b is an example of a firstcone face and the cone face 49 b is an example of a second cone face.

The hub 47 is coupled to the input shaft 21 to integrally rotate aboutthe first rotational center Ax1.

The sleeve 48 includes a pressing part 48 a that presses the pressedpart 49 a of the synchronizer ring 49. The pressing part 48 a is anannular flat face about the first rotational center Ax1. The sleeve 48is coupled to the hub 47 by spline coupling to rotate together about thefirst rotational center Ax1 and be movable relative to the hub 47 alongthe axis of the input shaft 21. That is, the sleeve 48 integrallyrotates with the input shaft 21 about the first rotational center Ax1and is movable along the axis of the input shaft 21.

To be specific, the sleeve 48 is movable along the axis of the inputshaft 21 between a press position (not illustrated) and a non-pressposition (FIG. 1). In the press position the sleeve 48 makes contactwith the synchronizer ring 49 while in the non-press position (FIG. 1)the sleeve 48 is separated from the synchronizer ring 49. In thenon-press position, the pressing part 48 a and the pressed part 49 a areseparated from each other and the sleeve 48 does not press the cone face49 b against the cone face 35 b. In the press position, the pressingpart 48 a and the pressed part 49 a contact with each other and thesleeve 48 presses the cone face 49 b against the cone face 35 b. Thepress position is closer to the drive gear 35 (right side in FIG. 1)than the non-press position. A second movement mechanism 50 moves thesleeve 48 between the press position and the non-press position. Thesecond movement mechanism 50 includes an actuator 50 a (FIG. 2) such asa motor and a transmission mechanism (not illustrated) that transmitsdriving power of the actuator 50 a to the sleeve 48. The non-pressposition is also referred to as a neutral position.

In the press position, the sleeve 48 presses the cone face 49 b againstthe cone face 35 b, placing the synchronizing mechanism 42 in the powertransmission state. In the non-press position the sleeve 48 does notpress the cone face 49 b against the cone face 35 b, placing thesynchronizing mechanism 42 in the power shut-down state.

In the transmission 12 as configured above, the sleeve 48 is movablefrom the non-press position to the press position while the clutchmechanism 41 transmits rotation between the input shaft 21 and the drivegear 33 and transmits no rotation between the input shaft 21 and thedrive gear 35. The clutch mechanism 41 can transmit rotation between theinput shaft 21 and the drive gear 33 while the sleeve 48 moves from thenon-press position to the press position.

FIG. 2 is an exemplary block diagram illustrating the schematicconfiguration of the vehicle 1 in the first embodiment. As illustratedin FIG. 2, the vehicle 1 includes a control device 14. The controldevice 14 and the transmission 12 constitute a power transmission system15.

The control device 14 is connected to the motor generator 11, theactuator 45 a of the first movement mechanism 45, and the actuator 50 aof the second movement mechanism 50 to control them. The control device14 is also connected to a storage device 55 and various sensors (notillustrated).

The control device 14 is, for example, an electronic control unit (ECU)including a processor such as a central processing unit (CPU). Theprocessor of the control device 14 executes operations in accordancewith a program installed in the storage device 55 to thereby implementvarious functions. The control device 14 can include hardware such as afield programmable gate array (FPGA) and an application specificintegrated circuit (ASIC), and the hardware may control the respectiveelements.

The control device 14 includes, as functions, a motor controller 14 a, aclutch controller 14 b, and a synchronous controller 14 c. Thesefunctions are implemented by the processor of the control device 14which executes the program installed in the storage device 55. In thefirst embodiment, part or all of these functions may be implemented bydedicated hardware (circuit). The motor controller 14 a controls themotor generator 11, the clutch controller 14 b controls the clutchmechanism 41, and the synchronous controller 14 c controls thesynchronizing mechanism 42.

The storage device 55 includes, for example, a read only memory (ROM)and a random access memory (RAM). The storage device 55 may include ahard disk drive (HDD) and a solid state drive (SSD). The various sensorsinclude a sensor that measures the speed of the vehicle 1, a sensor thatmeasures the stepping amount of an accelerator pedal, and sensors thatdetect the positions of the sleeves 44 and 48.

Next, acceleration processing to be executed by the control device 14 atthe time of a gear shift from the 1-speed gear 31 to the 2-speed gear 32during acceleration of the vehicle 1 traveling forward will be describedby way of example.

The acceleration processing is implemented in response to increase inthe amount (stroke) of the driver's stepping on the accelerator pedal.Through the processing, the control device 14 controls the motorgenerator 11, the synchronizing mechanism 42, and the clutch mechanism41 such that the acceleration of the vehicle 1 constantly exceeds zerowhile switching the 1-speed gear 31 to the 2-speed gear 32 duringacceleration of the vehicle 1. The control device 14 controls the motorgenerator 11, the synchronizing mechanism 42, and the clutch mechanism41 such that at least one of the synchronizing mechanism 42 and theclutch mechanism 41 constantly transmits power between the input shaft21 and the output shaft 22 during a gear shift from the 1-speed gear 31to the 2-speed gear 32, and that the motor generator 11 constantlygenerates torque for the period from start of the operation of each ofthe synchronizing mechanism 42 and the clutch mechanism 41 to the powertransmission state of the synchronizing mechanism 42.

Hereinafter, the acceleration processing will be described in detailwith reference to FIG. 3. FIG. 3 is an exemplary timing chartillustrating an example of the operation of the vehicle 1 in the firstembodiment.

In FIG. 3, line L1 indicates variation in the position of the sleeve 44of the clutch mechanism 41. Line L2 indicates variation in torque(hereinafter, also referred to as synchronous cone torque) that istransmitted between the cone face 49 b of the synchronizer ring 49 andthe cone face 35 b of the drive gear 35. Line L3 indicates variation intorque (hereinafter, also referred to as motor torque) generated by themotor generator 11. Line L4 indicates variation in the acceleration ofthe vehicle 1. Line L5 indicates variation in the rotation speed(rotation rate) of the shaft 11 a of the motor generator 11. Therotation speed (rotation rate) of the input shaft 21 varies similarly tothe line L5. In FIG. 3, time elapses from time t1 to time t6.

In the example of FIG. 3, before time t1, the sleeve 44 is located inthe 1-speed mesh position (1ST in FIG. 3) and the 1-speed gear 31 isselected. In this case, before time t2 the sleeve 48 is not located inthe press position and the synchronizing mechanism 42 generates nosynchronous cone torque. Before time t2, the control device 14 applies apredetermined positive voltage (current) to the motor generator 11 toaccelerate the vehicle 1, which increases the rotation speed of theshaft 11 a of the motor generator 11 over time.

When, for example, the rotation speed of the shaft 11 a of the motorgenerator 11 reaches a predetermined rotation speed while the 1-speedgear 31 is selected, the clutch controller 14 b controls the actuator 45a of the first movement mechanism 45 to move the sleeve 44 to thenon-mesh position (N in FIG. 3) from the 1-speed mesh position (1ST).Thereby, the sleeve 44 starts moving to the non-mesh position (N) fromthe 1-speed mesh position (1ST) at time t1 and reaches the non-meshposition (N) at time t2. Time t1 represents the operation start time ofthe clutch mechanism 41. As described above, between time t1 and t2 thesleeve 48 is not located in the press position and no synchronous conetorque is generated. The reason why the sleeve 44 can move from the1-speed mesh position (1ST) to the non-mesh position (N) under suchcondition is because both the one-way clutch 37 and the clutch mechanism41 (the hub 43 and the sleeve 44) or the one-way clutch 37 alonetransmits the rotation (power) from the input shaft 21 to the drive gear33. The sleeve 44 is located in the non-mesh position (N) from time t2to t4.

The synchronous controller 14 c controls the actuator 50 a of the secondmovement mechanism 50 to drive the synchronizing mechanism 42 to startgenerating the synchronous cone torque at time t2. The sleeve 48 of thesynchronizing mechanism 42 thereby starts moving from the non-pressposition to the press position from time t1 and reaches the pressposition at time t2, by way of example. The time t1 represents theoperation start time of the synchronizing mechanism 42 and time t2represents the time at which the synchronizing mechanism 42 is placed inthe power transmission state. From time t2 to t5, the synchronouscontroller 14 c controls the actuator 50 a to continuously apply forceto the sleeve 48 so that the sleeve 48 moves from the non-press positionto the press position. Thus, the synchronous cone torque rises over time(time t2 to t3). The synchronous cone torque reaches a predeterminedupper limit value (threshold) and becomes constant (time t2 to t4). Thepredetermined upper limit value represents maximum transmissible torque(permissible torque) between the cone face 49 b of the synchronizer ring49 and the cone face 35 b of the drive gear 35.

Next, the clutch controller 14 b controls the actuator 45 a of the firstmovement mechanism 45 to move the sleeve 44 from the non-mesh position(N) to the 2-speed mesh position (2ND in FIG. 3) at time t4 at which thesynchronous cone torque exhibits the upper limit value. The sleeve 44thereby starts moving from the non-mesh position (N) to the 2-speed meshposition (2ND) at time t4 and reaches the 2-speed mesh position (2ND) attime t5. That is, the gear is switched to the 2-speed gear 32 at timet5. In the first embodiment, the sleeve 44 is controlled to switch thegear to the 2-speed gear 32 before the synchronizing mechanism 42completely synchronizes the rotation of the drive gear 35 and therotation of the input shaft 21, that is, with a difference (differentialrotation) in the rotation speed between the drive gear 35 and the inputshaft 21.

The synchronous controller 14 c controls the actuator 50 a to drive thesleeve 48 to start moving from the press position to the non-pressposition for decreasing the synchronous cone torque, approximatelysimultaneously with the moving start of the sleeve 44 to the 2-speedmesh position (2ND) for the gear switch to the 2-speed gear 32 (timet5). The synchronous cone torque thereby falls to zero at time t6.

During the control over the sleeves, the motor controller 14 a controlsthe motor generator 11 as follows. The motor controller 14 a applies avoltage to the motor generator 11 to generate predetermined first motortorque before time t2 at which the synchronous cone torque is generated.That is, the motor controller 14 a controls the synchronizing mechanism42 and the clutch mechanism 41 to start operating at time t1, and thesynchronizing mechanism 42 to be placed in the power transmission stateat time t2, and controls the motor generator 11 to constantly generatetorque from time t1 to t2.

The motor controller 14 a controls the motor generator 11 to decreasethe motor torque from time t2 at which the synchronous cone torque isgenerated. The motor controller 14 a applies a voltage to the motorgenerator 11 to generate negative motor torque between time t3 and t4.For example, the motor controller 14 a applies a negative voltage to themotor generator 11 to generate negative torque. Thus, generated negativetorque can put a stop on the rotation of the shaft 11 a of the motorgenerator 11 and the input shaft 21, so that the rotation speed of theinput shaft 21 and the rotation speed of the drive gear 35 approach eachother in a shorter period of time.

Subsequently, the motor controller 14 a controls the motor generator 11to increase the first motor torque to predetermined second torque largerthan the first motor torque between time t4 to t6. To be specific, themotor controller 14 a controls the motor generator 11 such that theincrease rate of the motor torque is higher in the period of time t5 tot6 than in the period of time t4 to t5.

Through such motor torque control, the rotation speed of the shaft 11 aof the motor generator 11 rises till past time t3 and decreases in theperiod of time t3 to t5, and rises again after time t5. When the motorgenerator 11 is an AC motor generator, motor controller 14 a (thecontrol device 14) controls the motor torque and the rotation speed ofthe motor generator 11 via the inverter.

Through the control and the operations of the respective elements, thepower is transmitted between the input shaft 21 and the output shaft 22and between the motor generator 11 and the wheels 13L and 13R from startof the switch or shift of the gear at time t1 to completion of the gearswitch or shift at time t6. To be specific, from start of the gearswitch at time t1 to rising of the synchronous cone torque of thesynchronizing mechanism 42 at time t2, at least the one-way clutch 37transmits power between the input shaft 21 and the drive gear 33 andbetween the input shaft 21 and the output shaft 22. In the period oftime t2 to t6, at least the synchronizing mechanism 42 applies thesynchronous torque to transmit the power between the input shaft 21 andthe drive gear 35 and between the input shaft 21 and the output shaft22. In the period of time t5 to t6, the clutch mechanism 41 alsotransmits the power between the input shaft 21 and the drive gear 35.Through these operations, the acceleration of the vehicle 1 exceeds zerofrom start to completion of the gear switch or shift at time t1 to timet6.

As described above, according to the power transmission system 15 in thefirst embodiment, the control device 14 controls the motor generator 11,the synchronizing mechanism 42, and the clutch mechanism 41 such thatthe acceleration of the vehicle 1 constantly exceeds zero while the1-speed gear 31 is switched to the 2-speed gear 32 during accelerationof the vehicle 1. The control device 14 controls at least one of thesynchronizing mechanism 42 and the clutch mechanism 41 to constantlytransmit the power between the input shaft 21 and the output shaft 22during the gear switch from the 1-speed gear 31 (first-speed gear) tothe 2-speed gear 32 (second-speed gear), and controls the motorgenerator 11 to constantly generate torque from the operation start ofeach of the synchronizing mechanism 42 and the clutch mechanism 41 tothe power transmission state of the synchronizing mechanism 42.

This configuration can prevent impact from being applied on the vehicle1 during the gear switch, for example. In the gear switch from the1-speed gear 31 to the 2-speed gear 32 during the acceleration of thevehicle 1, the acceleration of the vehicle 1 can be prevented fromfalling to zero.

In the power transmission system 15, while the clutch mechanism 41transmits rotation between the input shaft 21 (first shaft) and thedrive gear 33 (first gear) and transmits no rotation between the inputshaft 21 and the drive gear 35 (third gear), the sleeve 48 is movablefrom the non-press position to the press position. The clutch mechanism41 can transmit rotation between the input shaft 21 and the drive gear33 while the sleeve 48 moves from the non-press position to the pressposition. With such a configuration, for example, at the time of a gearswitch from the 1-speed gear 31 to the 2-speed gear 32 for accelerationof the vehicle 1, no power transmission between the input shaft 21 andthe output shaft 22 can be prevented.

In the power transmission system 15, for example, the power of the motorgenerator 11 is transmitted from one of the input shaft 21 and the drivegear 33 (the input shaft 21 as an example) to the other (the drive gear33 as an example) through the clutch mechanism 41, to normally (firstdirection) rotate the input shaft 21 and the drive gear 33. The clutchmechanism 41 includes the one-way clutch 37 that is interposed betweenthe input shaft 21 and the drive gear 33 to transmit normal rotationfrom the one (input shaft 21) to the other (drive gear 33), and permitsnormal rotation of the other (drive gear 33) relative to the one (inputshaft 21). Thereby, the one-way clutch 37 can transmit rotation betweenthe input shaft 21 and the drive gear 33 while the sleeve 48 moves fromthe non-press position to the press position.

Second Embodiment

FIG. 4 is an exemplary diagram illustrating the schematic configurationof a vehicle 1 in a second embodiment. The vehicle 1 in the secondembodiment is configured similarly to the vehicle 1 in the firstembodiment. The second embodiment can thus attain similar effects basedon the similar configurations, as with the first embodiment. In thefollowing, the differences from the vehicle 1 in the first embodimentwill be mainly described.

In the second embodiment, the vehicle 1 includes a synchronizingmechanism 42A instead of the synchronizing mechanism 42 in the firstembodiment. The synchronizing mechanism 42A is located between the inputshaft 21 and the drive gear 35. As with the synchronizing mechanism 42,the synchronizing mechanism 42A is switched between a power transmissionstate and a power shut-off state. In the power transmission state thesynchronizing mechanism 42A generates friction force to allow therotation speed of the input shaft 21 and the rotation speed of the drivegear 35 to approach each other. In the power shut-off state thesynchronizing mechanism 42A generates no friction force. Thesynchronizing mechanism 42A can synchronize the rotation of the drivegear 35 and the rotation of the input shaft 21 by the friction force.

The synchronizing mechanism 42A includes a hub 43, a sleeve 44, and asynchronizer ring 49A. Thus, the hub 43 and the sleeve 44 are commonlyused by the synchronizing mechanism 42A and the clutch mechanism 41. Inthe second embodiment, with no actuator 50 a provided, the actuator 45 ais commonly used by the synchronizing mechanism 42A and the clutchmechanism 41. The sleeve 44 is an example of a first sleeve and a secondsleeve.

The synchronizer ring 49A is located between the sleeve 44 and the drivegear 35, and is rotatable relative to the drive gear 35 and movablealong the axis of the input shaft 21.

The synchronizer ring 49A includes a cone face 49 b and teeth 49 c. Theteeth 49 c have chamfers that are pressed by chamfers of the teeth 44 bof the sleeve 44. The chamfers of the teeth 49 c are pressed by thechamfers of the teeth 44 b of the sleeve 44 moving from the non-meshposition (1-speed mesh position) to the 2-speed mesh position, therebypressing the cone face 49 b against the cone face 35 b of the drive gear35 to generate friction force between the cone face 49 b and the coneface 35 b. This position of the sleeve 44 is a press position. By thefriction force, the rotation of the drive gear 35 and the rotation ofthe input shaft 21 are synchronized with each other. After thesynchronization, the teeth 44 b of the sleeve 44 pass between the teeth49 c of the synchronizer ring 49A and mesh with the teeth 35 a of thedrive gear 35. Thus, while moving from the non-mesh position to the2-speed mesh position, the sleeve 44 pushes the synchronizer ring 49A soas to press the cone face 49 b against the cone face 35 b. In the secondembodiment, the non-mesh position or the 1-speed mesh position is anexample of a non-press position.

As configured above, while the clutch mechanism 41 transmits rotationbetween the input shaft 21 and the drive gear 33 and transmits norotation between the input shaft 21 and the drive gear 35, the sleeve 44is movable from the non-mesh position, i.e., the non-press position tothe press position. The one-way clutch 37 of the clutch mechanism 41 cantransmit rotation between the input shaft 21 and the drive gear 33 whilethe sleeve 44 moves from the non-mesh position to the press position.The control device 14 hence controls the actuator 45 a to move thesleeve 44 from the non-mesh position (non-press position) to the pressposition, whereby at least one of the synchronizing mechanism 42A andthe clutch mechanism 41 can constantly transmit the power between theinput shaft 21 and the output shaft 22 during a gear switch from the1-speed gear 31 to the 2-speed gear 32.

As with the first embodiment, the control device 14 controls the motorgenerator 11, the synchronizing mechanism 42A, and the clutch mechanism41 such that the acceleration of the vehicle 1 constantly exceeds zerowhile the 1-speed gear 31 is switched to the 2-speed gear 32 duringacceleration of the vehicle 1.

The control device 14 controls the motor generator 11, the synchronizingmechanism 42A, and the clutch mechanism 41 such that at least one of thesynchronizing mechanism 42A and the clutch mechanism 41 constantlytransmits the power between the input shaft 21 and the output shaft 22during a gear shift from the 1-speed gear 31 to the 2-speed gear 32, andthat the motor generator 11 constantly generates torque for the periodfrom start of the operation of each of the synchronizing mechanism 42and the clutch mechanism 41 to the power transmission state of thesynchronizing mechanism 42. Specifically, the control device 14 appliesa voltage to the motor generator 11 for the period from the operationstart of the synchronizing mechanism 42A and the clutch mechanism 41 tothe contact between the cone face 49 b and the cone face 35 b, placingthe synchronizing mechanism 42A in the power transmission state.

As described above, according to the second embodiment, the sleeve 44and the actuator 45 a are commonly used by the synchronizing mechanism42A and the clutch mechanism 41, thereby enabling simplification anddownsizing of the structure of the transmission 12.

Third Embodiment

FIG. 5 is an exemplary diagram illustrating the schematic configurationof the vehicle 1 in a third embodiment. The vehicle 1 in the thirdembodiment is configured similarly to the vehicles 1 in the first andsecond embodiments. The third embodiment can thus attain similar effectsbased on the similar configurations as the first and second embodiments.Hereinafter, the differences from the vehicle 1 in the second embodimentwill be mainly described.

In the third embodiment, the vehicle 1 includes a sleeve 44A instead ofthe sleeve 44 of the clutch mechanism 41 and the synchronizing mechanism42A in the second embodiment. The one-way clutch 37 is omitted. Thesleeve 44A is an example of a first sleeve and a second sleeve.

The sleeve 44A includes a 1-speed movable part 44 d, a 2-speed movablepart 44 c, and a plurality of elastic members 71. The 1-speed movablepart 44 d is an example of a first movable part and the 2-speed movablepart 44 c is an example of a second movable part.

The 2-speed movable part 44 c is a sleeve and includes teeth 44 b. The2-speed movable part 44 c is located between the drive gear 33 and thedrive gear 35.

The 2-speed movable part 44 c is coupled to the hub 43 by splinecoupling to integrally rotate about the first rotational center Ax1 andbe movable along the axis of the input shaft 21 relative to the hub 43.That is, the 2-speed movable part 44 c and the input shaft 21 integrallyrotate about the first rotational center Ax1 and the 2-speed movablepart 44 c is movable along the axis of the input shaft 21. To bespecific, the 2-speed movable part 44 c is movable along the axis of theinput shaft 21 between a 2-speed mesh position and a non-mesh position(FIG. 5) closer to the drive gear 33 than the 2-speed mesh position. Inthe 2-speed mesh position the teeth 44 b and the teeth 35 a mesh witheach other while in the non-mesh position the teeth 44 b and the teeth35 a do not mesh with each other.

The 2-speed movable part 44 c pushes the synchronizer ring 49A so as topress the cone face 49 b against the cone face 35 b while moving fromthe non-mesh position to the 2-speed mesh position. This generatesfriction between the cone face 49 b and the cone face 35 b. Thisposition of the 2-speed movable part 44 c is a press position. By thefriction force, the rotation of the drive gear 35 and the rotation ofthe input shaft 21 are synchronized with each other. After thesynchronization, the teeth 44 b of the 2-speed movable part 44 c passbetween the teeth 49 c of the synchronizer ring 49A and mesh with theteeth 35 a of the drive gear 35. The 2-speed movable part 44 c is drivenby the actuator 45 a. In the third embodiment, the non-mesh position isan example of a non-press position and the 2-speed mesh position is anexample of a mesh position.

The 1-speed movable part 44 d is a sleeve and includes the teeth 44 a.The 1-speed movable part 44 d is larger in diameter than the 2-speedmovable part 44 c. In FIG. 5, the 1-speed movable part 44 d issubstantially the same in diameter as the 2-speed movable part 44 c forthe sake of convenience. The 1-speed movable part 44 d is, for example,coupled to the 2-speed movable part 44 c by spline coupling tointegrally rotate about the first rotational center Ax1 and be movablealong the axis of the input shaft 21 relative to the 2-speed movablepart 44 c. That is, the 1-speed movable part 44 d and the input shaft 21integrally rotate about the first rotational center Ax1 and the 1-speedmovable part 44 d is movable along the axis of the input shaft 21. To bespecific, the 1-speed movable part 44 d is be movable along the axis ofthe input shaft 21 between a 1-speed mesh position and a non-meshposition closer to the drive gear 35 than the 1-speed mesh position. Inthe 1-speed mesh position the teeth 44 a and the teeth 33 a mesh witheach other while in the non-mesh position the teeth 44 a and the teeth33 a do not mesh with each other. The 1-speed mesh position is anexample of a mesh position and the non-mesh position is an example of anon-press position.

The elastic members 71 represent coil springs. The elastic members aredisposed with spacing about the first rotational center Ax1 and connectthe 1-speed movable part 44 d and the 2-speed movable part 44 c. Theelastic members 71 generate force (elastic force) to move the 1-speedmovable part 44 d to the non-mesh position (left side in FIG. 5) whenthe 1-speed movable part 44 d is located in the mesh position (FIG. 5)and the 2-speed movable part 44 c is located in the non-mesh position.That is, the elastic members 71 generate force to move the 1-speedmovable part 44 d toward the 2-speed movable part 44 c. The elasticmembers 71 are an example of a driver. The number of elastic members 71may be one. The driver may include an actuator.

As configured above, in switching the gear from the 1-speed gear 31 tothe 2-speed gear 32, the actuator 45 a drives the 2-speed movable part44 c to move from the non-mesh position to the 2-speed mesh position andpush the synchronizer ring 49A so as to press the cone face 49 b againstthe cone face 35 b, generating friction force between the cone face 49 band the cone face 35 b. This reduces the rotation speed of the shaft 11a and the rotation speed of the drive gear 33, decreasing the power tobe transmitted between the teeth 44 a of the 1-speed movable part 44 dand the teeth 33 a of the drive gear 33. By the elastic force of theelastic members 71, the 1-speed movable part 44 d is then separated fromthe teeth 33 a of the drive gear 33 and moves to the non-mesh position.Thus, the elastic members 71 move the 1-speed movable part 44 d to thenon-mesh position by the elastic force, along with the motion of the2-speed movable part 44 c to the mesh position to press the cone face 49b against the cone face 35 b. Thus, the control device 14 controls theactuator 45 a to move the 2-speed movable part 44 c from the non-pressposition to the press position, whereby at least one of thesynchronizing mechanism 42A and the clutch mechanism 41 constantlytransmits the power between the input shaft 21 and the output shaft 22during the gear switch from the 1-speed gear 31 to the 2-speed gear 32.

As with the first and second embodiments, the control device 14 of thethird embodiment controls the motor generator 11, the synchronizingmechanism 42A, and the clutch mechanism 41 such that the acceleration ofthe vehicle 1 constantly exceeds zero while the 1-speed gear 31 isswitched to the 2-speed gear 32 during the acceleration of the vehicle1.

The control device 14 controls the motor generator 11, the synchronizingmechanism 42A, and the clutch mechanism 41 such that at least one of thesynchronizing mechanism 42A and the clutch mechanism 41 constantlytransmits the power between the input shaft 21 and the output shaft 22during a gear shift from the 1-speed gear 31 to the 2-speed gear 32, andthat the motor generator 11 constantly generates torque for the periodfrom start of the operation of each of the synchronizing mechanism 42and the clutch mechanism 41 to the power transmission state of thesynchronizing mechanism 42. Specifically, the control device 14 appliesa voltage to the motor generator 11 for the period from the operationstart of each of the synchronizing mechanism 42A and the clutchmechanism 41 to the contact between the cone face 49 b and the cone face35 b, allowing the synchronizing mechanism 42A to generate frictionforce (power transmission state).

As described above, the vehicle 1 of the third embodiment includes the1-speed movable part 44 d (first movable part), the 2-speed movable part44 c (second movable part), and the elastic members 71 (driver).Thereby, the 1-speed movable part 44 d can transmit rotation between theinput shaft 21 and the drive gear 33 while the 2-speed movable part 44 cmoves to the press position from the non-mesh position being thenon-press position.

The first to third embodiments have described the example that the drivegears 33 and 35 are rotatable relative to the input shaft 21 and thedriven gears 34 and 36 are fixed to the output shaft 22 to rotatetogether. However, the invention is not limited to such an example.Alternatively, the drive gears 33 and 35 may be fixed to the input shaft21 to integrally rotate while the driven gears 34 and 36 may berotatable relative to the output shaft 22. In this case, the outputshaft 22 (first shaft) is provided with the synchronizing mechanism 42or 42A and the clutch mechanism 41. Also, the power of the motorgenerator 11 is transmitted from the driven gear 34 (one) to the outputshaft 22 (the other) through the clutch mechanism 41.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel methods and systems describedherein may be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the methods andsystems described herein may be made without departing from the spiritof the inventions. The accompanying claims and their equivalents areintended to cover such forms or modifications as would fall within thescope and spirit of the inventions.

What is claimed is:
 1. A power transmission system, comprising: atransmission that is located between a motor generator and a wheel bothof which are mounted on a vehicle; and a control device, wherein thetransmission includes: a first shaft that is rotatable; a second shaftthat is rotatable and parallel to the first shaft; a first-speed gearhaving a first gear and a second gear, the first gear rotatably attachedto the first shaft, the second gear attached to the second shaft to meshwith the first gear and integrally rotate with the second shaft; asecond-speed gear being smaller in gear ratio than the first-speed gearand having a third gear and a fourth gear, the third gear rotatablyattached to the first shaft, the fourth gear attached to the secondshaft, to mesh with the third gear and integrally rotate with the secondshaft; a synchronizing mechanism that is interposed between the firstshaft and the third gear and to be switched between a power transmissionstate and a power shut-off state, the power transmission state being astate in which the synchronizing mechanism generates friction force thatcauses a rotation speed of the first shaft and a rotation speed of thethird gear to approach each other, the power shut-off state being astate in which the synchronizing mechanism generates no friction force;and a clutch mechanism that switches transmission and non-transmissionof rotation between the first shaft and the first gear and between thefirst shaft and the third gear, one of the first shaft and the secondshaft is connected to the motor generator and the other is connected tothe wheel, and the control device controls the motor generator, thesynchronizing mechanism, and the clutch mechanism such that at least oneof the synchronizing mechanism and the clutch mechanism constantlytransmits power between the first shaft and the second shaft during agear switch from the first-speed gear to the second-speed gear, and thatthe motor generator constantly generates torque for a period from wheneach of the synchronizing mechanism and the clutch mechanism startsoperating to when the synchronizing mechanism is placed in the powertransmission state.
 2. The power transmission system according to claim1, wherein the synchronizing mechanism includes: a first cone face ofthe third gear, that integrally rotates with the third gear; asynchronizer ring having a second cone face that is pressed against thefirst cone face to generate friction force with the first cone face; anda first sleeve that is movable along an axis of the first shaft betweena press position and a non-press position, and integrally rotates withthe first shaft, the press position being a position in which the secondcone face is pressed against the first cone face, the non-press positionbeing a position in which the second cone face is not pressed againstthe first cone face, the first sleeve is movable from the non-pressposition to the press position while the clutch mechanism transmitsrotation between the first shaft and the first gear and transmits norotation between the first shaft and the third gear, and the clutchmechanism is configured to transmit rotation between the first shaft andthe first gear while the first sleeve moves from the non-press positionto the press position.
 3. The power transmission system according toclaim 1, wherein the first shaft and the first gear are rotated in afirst direction by power of the motor generator, and the clutchmechanism includes a one-way clutch that is located between the firstshaft and the first gear, transmits rotation in the first direction fromthe one of the first shaft and the second shaft to the other, and allowsthe other to rotate in the first direction relative to the one of thefirst shaft and the second shaft.
 4. The power transmission systemaccording to claim 2, wherein the first-speed gear and the second-speedgear are spaced apart from each other along the axis of the first shaft,and the clutch mechanism includes: first teeth that integrally rotatewith the first gear; second teeth that integrally rotate with the thirdgear; a first movable part that includes third teeth, is located betweenthe first gear and the third gear, is movable along the axis of thefirst shaft between a first mesh position and a first non-mesh position,and integrally rotates with the first shaft, the first mesh positionbeing a position in which the third teeth and the first teeth mesh witheach other, the first non-mesh position being closer to the third gearthan the mesh position and being a position in which the third teeth andthe first teeth do not mesh with each other; a second movable part thatincludes fourth teeth, is located between the first gear and the thirdgear, is movable along the axis of the first shaft between a second meshposition and a second non-mesh position and integrally rotates with thefirst shaft, and presses the second cone face against the first coneface while moving from the second non-mesh position to the second meshposition, the second mesh position being a position in which the fourthteeth and the second teeth mesh with each other, the second meshposition being closer to the first gear than the mesh position, andbeing a position in which the fourth teeth and the second teeth do notmesh with each other; and a driver that connects the first movable partand the second movable part, generates force to move the first movablepart to the first non-mesh position when the first movable part islocated in the first mesh position and the second movable part islocated in the second non-mesh position, and moves the first movablepart to the non-mesh position by the force along with the motion of thesecond movable part to the second mesh position to press the second coneface against the first cone face.